1. Field of the Invention.
The present invention relates to axial fans and, particularly, to a construction for securing individual fan blade assemblies within apertures in a fan hub whereby the blade assemblies are centered within the hub apertures and the fan, itself, is statically and dynamically balanced.
2. Description of the Prior Art.
Axial fan constructions wherein individual blade assemblies are secured within apertures in the fan hub are known to the prior art. An example of such a construction is shown in the U.S. Pat. No. 3,545,884, issued Dec. 8, 1970, for ADJUSTABLE FAN CONSTRUCTION to J. W. Schroeter et al. The Schroeter et al. construction employs an air foil extending from a base with the base having a cylindrical portion which fits into a counterbore in a fan hub assembly. The cylindrical portion provides a shoulder in opposing relation to a face of the counterbore with a resilient member being positioned between the counterbore face and base shoulder. A retaining disc allows a clamping action to secure the blade assembly to the hub by bolts extending between the disc and the blade base.
The Schroeter et al. construction positions a spacer between the retaining disc and blade base to allow a prestressing of the bolts while limiting the amount of compression of the resilient member. In this manner, the bolts that secure the blade assembly to the hub may be prestressed to counter fatigue failure while the limit on compression in the resilient member limits the force necessary to realign the blade relative to the hub. Thus, it is possible to securely clamp the blade assembly to the hub while allowing a manual adjustment of the blade assembly.